Vehicle seats are often occupied for extended periods of time and it is therefore desirable that they should be adjustable in position and/or in the relative disposition of their parts so that the occupants of a seat can choose the most comfortable arrangement to suit his or her anatomy and for different purposes such as sleeping or reading. To this end, vehicle seats are often made with adjustable parts which can be fixed in different positions so that occupants can adopt various upright or reclined postures. For example, seats may have hinged back supports which can be fixed at different inclinations, sometimes with simultaneous tilting of the seat bottom.
Operational requirements of vehicles, however, place limitations on the extent to which adjustability can be provided. For example, in commercial aircraft, operating costs are such that the space between rows of seats should be minimal compatible with providing degrees of passenger comfort appropriate to certain recognised classes of fare. Fares are naturally related to the number of passengers that can be accommodated in an aircraft, so the spacing of seat rows is a crucial factor in determining fares. Improving comfort without increasing the spacing of seat rows, or reducing the spacing whilst maintaining comfort can thus have important advantages for the aircraft operator. However, with current designs of adjustable seat, this minimal row spacing may limit the angle through which a back support can be permitted to be moved between upright and reclining positions. It may also preculde the provision of support for the legs of seat occupants, which is desirable for maximum comfort to be achieved when a back support is inclined backwardly to allow the occupant of a seat to adopt a reclining posture.